In a small saucepan, whisk together the Thai chili sauce and peanut butter. Bring the mixture to a simmer and heat for 2 to 5 minutes, or until the peanut butter is fully incorporated and the sauce is smooth and creamy. Remove from heat and set aside.

In a wok or large saucepan, heat 3 inches (7.5 cm) of canola oil to 350°F (175°C). Use a candy thermometer or test with a small drop of batter—it should bubble up and fry quickly. Line a plate with paper towels.

In a medium bowl, whisk together the flour, cornmeal or polenta, cornstarch, salt, and pepper. Gradually whisk in the seltzer water until a thick batter forms.

Working in batches, add half of the cauliflower florets to the batter, ensuring each piece is fully coated. Use tongs to shake off any excess batter, then carefully place the florets into the hot oil one at a time. Fry for 4 to 6 minutes, or until golden brown. Transfer to the paper towel-lined plate to drain. Repeat with remaining cauliflower.

Once all the cauliflower has been fried, transfer it to a large bowl. Pour the peanut-chili sauce over the cauliflower and toss to coat evenly.

To build each taco, start with a warm tortilla. Add about 2 tablespoons of shredded carrots, 2 tablespoons of shredded cabbage, 6 to 8 pieces of coated cauliflower, and top with scallions, crushed peanuts, and sesame seeds if desired. Serve warm.